Hair drug testing untangled

What hair testing can – and can’t - tell us about a person’s drug and alcohol use .

Hair drug testing can be the make-or-break evidence needed in family court cases. Your clients may expect a testing report to be interpreted as black or white: a clear-cut yes or no statement. The reality is that a hair drug test report reveals far more than what’s going on in the here and now. It contains a wealth of trended information that can be used to help a family court reach decisions, for instance about childcare arrangements.

It can therefore be helpful for family law practitioners to understand factors that can influence results, and what to do if they are faced with two conflicting reports from two different laboratories.

Which drugs can labs test for?

The most requested hair drug tests by a family court are for alcohol, then cannabis and cocaine. Labs can cater for a very wide range of drugs in hair, and are constantly expanding their test portfolios, often in line with “trends” in drug abuse. In addition to the drug groups listed above, we are currently seeing increases in requests for Ketamine and Psilocybin (magic) mushrooms and a slight decrease in testing for novel psychoactive substances (NPS).

At Cansford, we have recently extended our in-house testing to include a variety of prescription medications commonly used to treat clinical depression, anxiety, and OCD. Government statistics and our day-to-day dealings with family law professionals have shown a rise in mental ill health over the last 18 months through the Covid-19 pandemic. Family law cases may require a parent to demonstrate they have depression or anxiety under control, which has led to a need for wider drug testing capabilities.

We are also witnessing an increase in demand for steroid testing. Figures for steroids have been steadily climbing for years, but trends are indicating we may be about to see an explosion in use. Council-run needle exchanges in England and Wales have reported a huge surge in contact with users of steroids, and steroid abuse can be a factor reported in domestic abuse cases.

Why use hair testing?

Prior to the advent of hair testing, blood and urine were the samples used for detecting drugs and alcohol.

Blood only shows any substances in the subject in the few hours before the time of collection, and what is affecting their behaviour. Urine is still a popular sample: it is (usually) plentiful in supply and has a longer window of detection – usually half a day to five days after ingestion of the drug.

However, because of its ability to reveal the history of drug use over several months, hair is often the sample of choice. This is because it acts as a tape recorder that is constantly running, recording episodes of drug taking as they happen, and locking the information in place.

How do drugs get into hair?

Any drug entering the bloodstream constantly bathes the roots of the hair follicles around the body. The fraction of hair that is actively growing – known as anagen hair – takes up the drug from the bloodstream. Also present in the bloodstream are the metabolites of the drugs, formed by the body to make them more water soluble and excretable. The detection of metabolites is one way we confirm drug use. Drugs and metabolites can also get into hair via sweat and other secretions, particularly from the sebaceous glands.

When contamination is a possibility, the detection – or non-detection – of metabolites in the hair is useful to differentiate external contamination from ingestion. When the parent drug is detected without the detection of a metabolite, there is inevitably doubt about whether the drug has been taken. The presence of only the parent drug may just indicate exposure. Washing the hair sample removes any drug adhering to the surface and provides a way to assess the possibility of contamination over ingested drugs.

Put simply: if there is drug in the wash and no drug in the hair, then contamination is the probable cause rather than drug use.

Why do hair drug test results sometimes vary?

Hair is not a homogenous material. The hair growth cycle consists of three phases: the anagen phase (growth), the catagen phase (transition) and the telogen phase (resting). A typical head of hair will feature a combination of these phases.

Typically, 85% of hair is actively growing and 15% resting at any given time, but these proportions are variable. If a person has shaved their head, for example, then the hair growing will all be in the anagen phase. In a hair sample taken for testing, the proportions may not match the 85/15% ratios, and multiple samples are unlikely to contain anagen and telogen hair in the exact same proportions.

A hair sample can also be taken in different ways, which can have an impact on the test results. Some laboratories use a collection method where a lock of hair is separated, curled up on itself, and secured with a rubber band as close to the scalp as possible to ensure a close clip. However, collecting the sample in this way creates a cone effect, and it is virtually impossible to achieve a straight line cut. A straight cut is required to accurately segment the hair so that it shows substance usage in different time periods, and the “cone” approach can account for variation in results.

Hair growth rates can also have a significant impact on test results. The average hair growth rate is 1cm per month but in reality, this can vary substantially from 0.7cm to 1.5cm. Other genetic and external variables can also have an impact, such as seasonal variations, age, or if the donor is pregnant at the time of testing.

Can you predict drug dosage?

The concentration of drug measured in a donor’s hair does not accurately predict the dose of drug used, but it is possible to track changes of dose in an individual and therefore identify trends of drug use. So segmented hair analysis can be used to show increasing – or decreasing – use.

Once drugs have entered the hair shaft they are locked into place and the hair becomes a recorder of drug use over time. However, anything that damages the surface of the hair over time will cause drugs to leach out, for example hair dyes, which are generally found to reduce drug content in hair by around 40%. In the extreme, continued use of hair dyes and bleaches can reduce drugs in hair to undetectable levels.

This is important for labs and sample collectors to be aware of, so that they can take action to check drug use by other means, for example sampling body hair as opposed to head hair or returning for a surprise collection a couple of weeks later when new hair has grown. Nails can also be used if there is no suitable hair for analysis.

Can hair testing show whether someone has stopped using drugs?

Once a drug is in someone’s system, it is distributed across different phases of hair growth. There is a proportion of rapidly growing hair that will contain less of the drug, and as you move through a typical hair growth rate of 1cm per month, existing hair will contain more drug than any new growth.

The telogen (resting) phase can still contain a drug several months after drug use has stopped. The amount of drug will be less, but it will still be present. It is not possible to exclude use of drugs until it disappears from the hair completely.

It is possible to strongly imply abstinence because drug content in hair falls rapidly when drug use stops. In the month after abstinence begins, it is usual to see the drug concentration at 10-15% of previous levels, implying that the donor has stopped using drugs.

However, testing a person for abstinence after a period of drug use requires an interval of at least three to four months to be confident that the donor has stopped using. Testing before this time has elapsed will show movement in the right direction (or not) but cannot prove cessation of drug use.

A single hair drug testing report is a record of a moment in time, which is unlikely to provide a conclusive black or white answer about ongoing substance misuse. Hair drug testing is used to its best advantage to help establish trends over time and can tell you whether somebody’s drug usage levels have increased, decreased, or remained the same over a six-month period.